Old round pound coins will cease to be legal tender this weekend - but some shops will still be accepting them after the deadline.
From midnight on Sunday October 15, the round pound will lose its legal tender status, meaning stores cannot hand out old pound coins as change and can refuse to accept them as payment.
People have been urged to rummage through their wallets, coat pockets, piggy banks and sofas so that they can spend them, bank them or give them to charity before this date.
However, discount retailer Poundland has said more than 850 of its stores across the country will continue accepting the coins until October 31.
And a trade association representing small shops has advised its members to continue accepting the round coins to provide a "useful community service" to customers.
A spokesman for the Federation of Small Businesses told the Telegraph: "Shopkeepers will be aware that the Royal Mint has this deadline but at the same time they will not want to let their loyal customers down by saying they cannot pay with a round pound if they do not have any other change.
"It would help if small firms knew they were allowed a short transition period to collect the old coins if they wish to and are willing to bank them, but not give out to customers.
"This would provide a useful community service, allowing customers a few weeks to get rid of the final few pound coins in circulation."
Major banks have said that while they encourage customers to allow enough time to hand in their old coins, they will continue to accept deposits of round pounds from their customers after October 15.
People may also find they can still hand in the old £1 coins at the Post Office after this date.
With just a week to go, around 500 million old round pounds are still in circulation.
Exchequer Secretary to the Treasury Andrew Jones said people have returned more than 1.2 billion of the old coins in the past six months.
He said: "The hard work of the British public has paid off and I am delighted that more than 1.2 billion round pound coins have been returned."
Chief executive and deputy master of the Royal Mint Adam Lawrence said: "The round pound has been in circulation for over 30 years but, as the deadline approaches, we are keen to encourage everyone to track down their final coins and use them.
"As the deadline is triggered, we are proud that the security features on the 12-sided £1 coin will help to safeguard our currency for years to come."
The new 12-sided pound coin, which resembles the old threepenny bit, entered circulation in March and boasts new high-tech security features to thwart counterfeiters.
The production of the new coins follows concerns about round pounds being vulnerable to sophisticated counterfeiters. Around one in every 30 old-style pound coins in people's change in recent years has been fake.
One pound coins were first launched on April 21 1983 to replace £1 notes. The Royal Mint has produced more than two billion round pound coins since that time.
The Post Office said customers can continue to deposit their old round pounds into any of their usual high street bank accounts through any post office - even after October 15 - "until further notice".
The Post Office is also taking part in "Pudsey's round pound countdown" - collecting old round £1 coins for BBC Children in Need.
Barclays said its own customers can continue to deposit their old round pounds into their accounts with it after October 15, but added: "We would recommend that customers allow sufficient time to return old coins rather than leave it until legal tender status is withdrawn."
RBS/NatWest, Santander, Nationwide Building Society and Lloyds Banking Group, which includes Halifax, also said they will continue to accept round pounds as deposits from their own customers after they cease to be legal tender.
RBS/NatWest also said it would encourage customers to try to hand in their old coins as soon as possible.